Mechanical Numerical Keypad with local Audio FX

The desire to make this little keypad came from idea to reuse a some of the parts from a broken keyboard someone gave me.

The extra little feature of having audio fx being played locally on the keyboard with each button press, was from one of the commenters on reddit related to a post. The sound files will be read from the placed SD card. Currently the audio that can be played is from 8 to 16 kHz kHz sample rate with 16 bit signed PCM.

The lower level sd card interface for the file system used in the project was made by Khaled Magdy in their post on

Top View

Bottom View

Issues as of 08/2025

• Current USB port part is not vertically offset, which collides with the PCB, read "Connectors" page in the schematic.
• Encoder for PC system audio still glitches at times, but its significantly better compared to previous build versions
• Audio streaming and polling of the key inputs is done on a single thread, resulting in less than satisfactory responsiveness

Future work

• Move to a MCU series that include SDIO for the SD card, has more flash to as to implement some sort of RTOS, and or has a second core to handle the audio streaming.
• General rework of the PCB, redesign of the audio front-end to have better amplification of the DAC data stream.